1. Field of the Invention
The present invention relates to methods of processing lead frames in which an electronic part such as an IC (Integrated Circuit) is sealed with resin, hereinafter simply referred to as a resin sealed lead frame, and apparatuses therefor. More specifically, the present invention relates to a method of processing resin sealed lead frames for cutting a prescribed portion of the resin sealed lead frame or separating each electronic section forming a product, on the resin sealed lead frame and an improvement of the apparatus for performing the method.
2. Description of the Background Art
A first type of prior art related to the present invention will now be described with reference to FIGS. 11 and 12A to 12C. FIG. 11 generally shows a processing apparatus for a resin sealed lead frame according to the first type of prior art. FIGS. 12A to 12C schematically show an arrangement of a so-called QFP (Quad Flat Package) type resin sealed lead frame A in which outer leads 3 protrude from four sides of a resin sealed molding or mold package 2 in which an electronic part 1 is sealed.
In a resin sealed lead frame A shown in FIGS. 12A to 12C, a lead frame body 4 and a die pad 6 for mounting an electronic part 1 are connected by a pinch lead 5. A dam bar 7 is provided for preventing melted resin material from flowing out of a mold cavity at the time of sealing the electronic part 1 with resin. A cavity 8 serves as a resin pool. Four electronic parts 1 are mounted to the lead frame body 4 and each part 1 is electrically connected to a prescribed outer lead.
For separating each electronic section or product from the resin sealed lead frame A, for example, various cutting steps, such as cutting of the cavity 8, cutting of the resin at the dam bar 7, cutting of the dam bar 7 itself, cutting of a tip connecting portion of the outer lead 3 and cutting of the pinch lead 5, must be performed.
A plurality of such cutting steps, for example, the above mentioned resin cutting step and the dam bar cutting step can be performed almost simultaneously, depending on the thickness, shape or the like of the lead frame body 4. At the same time, any unnecessary step should be eliminated. The above mentioned separation of each electronic section is performed by a lead processing apparatus having an upper mold or tool 9 and a lower mold or tool 10, for example as shown in FIG. 11.
The lead processing apparatus illustrated in FIG. 11 is structured to perform only the above mentioned cavity cutting step, the dam bar cutting step and the pinch lead cutting step. More specifically, the lead processing apparatus shown in FIG. 11 is provided with a structure of a so-called sequentially feeding mold and includes: an upper mold base 11; a punch holder 12 fixed to the upper mold base 11; a punch blade 13 fixed to the punch holder 12; a stripper blade 14 suspended from the punch blade 13, a cavity cutting punch 15 for cutting the cavity 8; a dam bar cutting punch 16 for cutting the resin at the dam bar 7; and a pinch lead cutting punch 17 for cutting the pinch lead 5.
Base portions of punches 15, 16 and 17 are fixed to the same punch holder 12 through the punch blade 13, and their tip blades are fitted onto a punch guide 18. Dies 19, 20 and 21 are arranged on the lower mold 10, respectively corresponding to punches 15, 16 and 17.
As shown in FIG. 11, the resin sealed lead frame A is fed to a prescribed position between the upper and lower molds 9 and 10, and the cutting steps are sequentially performed by the punches 15, 16, 17, and the dies 19, 20, 21 while sequentially feeding each electronic section on the resin sealed lead frame A. Thus, each electronic section is sequentially separated.
As described above, in the conventional lead processing apparatus, each punch used for cutting and separating the electronic sections or product from the resin sealed lead frame A, is integrally fixed to one mold base, and the die corresponding to the punch is integrally fixed to the other mold base.
When the leads of a different type of resin sealed lead frame are to be processed, the above described conventional lead processing apparatus cannot be directly used. Then, a different lead processing apparatus for the resin sealed lead frame must be provided, or any unnecessary punches and dies fixed to the mold base 11 must be removed so that different punches and different dies required for the lead processing can be integrally fixed to the mold base.
Providing a dedicated separate lead processing apparatus for every kind of resin sealed lead frame is very uneconomical, and changing of the punches and dies for every kind of resin sealed lead frame requires not only a laborious operation but also skill for the fine adjusting after the tool and die change.
A second type of prior art related to the present invention will now be described with reference to FIGS. 13A and 13B. It is noted that elements corresponding to those of the above described first type of prior art shown in FIGS. 12A to 12C are denoted by the same reference numerals. FIGS. 13A and 13B schematically show an exemplary arrangement of a resin sealed lead frame in which outer leads 3 protrude from two sides of a resin sealed molding 2 including an electronic part 1.
In the resin sealed lead frame according to the second type of prior art shown in FIGS. 13A and 13B, a cradle 4 and a die pad 6 for mounting the electronic part 1 are connected by a pinch lead 5. A dam bar 7 is further provided to prevent melted resin from flowing out of a mold cavity at the time of sealing the electronic part 1 with resin. A prescribed number of electronic parts 1 are mounted on a cradle 4 and each part is electrically connected to a prescribed inner lead 28.
For the step of separating each electronic section or product from the resin sealed lead frame, a lead processing apparatus having a so-called sequentially feeding mold is used. The sequentially feeding mold includes a punch and die for cutting and thereby performs each cutting step while sequentially feeding the resin sealed lead frame to a prescribed position between the punch and die. For example, the mold sequentially performs cutting of resin and removal of resin at the dam bar 7, cutting of the dam bar 7, cutting of a tip connecting portion of an outer lead 3, and cutting of the pinch lead 5 or the like.
It is noted that if a mold for bending the outer lead 3 is provided along with the above described mold for cutting, a step of bending the outer lead can be simultaneously or separately performed. However, as the bending of the lead is performed in a manner substantially similar to that of the above mentioned cutting steps, a further description thereof is not necessary.
In the conventional method of processing the lead or leads described with reference to FIGS. 13A and 13B, the products are pressed by cutting molds which are spaced by one pitch along the feeding path while sequentially feeding the products on the lead frame by a distance equal to one pitch. One pitch is defined as the on-center spacing between two neighboring products along the feeding path. In the final processing step, each product is sequentially cut and separated from the resin sealed lead frame to produce separate products. For increasing the production volume per period of time, the number of lead processing apparatuses having similar functions and structures must be increased. For example, to double the production volume in the same period of time, two lead processing apparatuses having similar structures must be provided, whereby the equipment costs, and the required space for the equipment is doubled.